| OIO | Object Input/ Output
| Others |
| OIO | Offentlig Information Online
| Others |
| OIO | Office Inventory Ordering
| Others |
| OIO | Office of Internal Operations
| Others |
| OIO | Office of International Operations
| Others |
| OIO | Office Of The Insurance Ombudsman
| Others |
| OIO | Oil Immersion Objective
| Others |
| OIO | Old IO Or
| Others |
| OIO | Oldtimer In Obwalden
| Others |
| OIO | Onderzoeker in Opleiding
| Others |
| OIO | Onderzoeker In Opleiding (PhD student; Research worker in training)
| Others |
| OIO | One Is One
| Others |
| OIO | Open Indirect Ophthalmoscope
| Others |
| OIO | Open Information Online
| Others |
| OIO | Open Infrastructure For Outcomes
| Others |
| OIO | Open Infrastructure Offering
| Others |
| OIO | Opening Imbalance Only
| Others |
| OIO | Operational Integration Office
| Others |
| OIO | Opportunities In Options
| Others |
| OIO | Oracle Inter Office
| Others |
| OIO | Orientation in Objects
| Others |
| OIO | Orthopaedic Institute of Ohio
| Others |
| OIO | Overseas Investment Office
| Others |